Frictional Forces: Static and Kinetic
Vložit
- čas přidán 1. 03. 2017
- Newton's first law tells us that an object in motion will remain in motion, but we don't really see that on earth, do we? If you throw a ball, or push a hockey puck, these things do eventually stop. Why? To answer this we must learn about static and kinetic friction!
Watch the whole Classical Physics playlist: bit.ly/ProfDavePhysics1
Modern Physics Tutorials: bit.ly/ProfDavePhysics2
Mathematics Tutorials: bit.ly/ProfDaveMaths
General Chemistry Tutorials: bit.ly/ProfDaveGenChem
Organic Chemistry Tutorials: bit.ly/ProfDaveOrgChem
Biochemistry Tutorials: bit.ly/ProfDaveBiochem
Biology Tutorials: bit.ly/ProfDaveBio
EMAIL► ProfessorDaveExplains@gmail.com
PATREON► / professordaveexplains
Check out "Is This Wi-Fi Organic?", my book on disarming pseudoscience!
Amazon: amzn.to/2HtNpVH
Bookshop: bit.ly/39cKADM
Barnes and Noble: bit.ly/3pUjmrn
Book Depository: bit.ly/3aOVDlT
this guy carried me through sophomore year chemistry and now he's carrying me through junior year physics
Same
so you read Tintin books?
@@floydwynn-jones4043 ii
@@floydwynn-jones4043 i
@@floydwynn-jones4043 i
I did a short experiment. I watched this video 2 times: yesterday night and tonight.
Yesterday, I understood everything he said but couldn't get anything inside my head. So I used the whole day today to read the book and solved many maths related to frictions.
Tonight as I watched this video again I was able to understand everything loud and clear😁. Thanks professor Dave
This is like a crash course but nothing about it is too clumped. Perfect, straight-to-the-point, and easy. Will subscribe and listen to you religiously throughout my physics course. Thank you.
czcams.com/video/DE6QvdAO9Qw/video.html
Reason of why static friction is more than kinetic or dynamic friction
Professor Dave, your videos got me through physics 1 and 2 in my post-bacc, and as I'm studying for the MCAT I found myself needing additional explanation. The jingle came to my mind and I knew exactly where to go. So thankful for you and your videos!
I think of the formula for heat in terms of mass, temperature and specific heat, when I think of MCAT. Q=m*c*∆T
the jingle lol
Is it sad or impressive Dave can teach in 5 minutes what my professor can’t in 3 3 hour class periods?
Both. Impressive for Dave but sad for your professor and you guys. I'm in the same boat with my professor. His lectures are really disorganized. I was getting a little scared that I was getting confused so early in the semester, especially when I'm way ahead of the math requirements. Watching just a few of Dave's videos and I feel much more confident. I've learned more from from short CZcams videos than from 2 hour lectures.
YESSSSSSSSSSSSSSSSSSSSS
dude thats literally what happened to me in class. 3 hour class, dont understand much. i watch this, and it makes a lot of sense.
@Learn First very true, they want you to know how to do problems and smart students will read about it more at home
Am i the only kid watching this...
thanks a lot bro. this new subscriber is from the Philippines, the way you deliver the topic is so smooth, wonderful and easy to understand. thanks a lot. static & kinetic friction topic. great!
I swear without this video I would be super lost in my physics class
Unfortunately, my prof doesn't teach anything... so I am very thankful for your videos with visual aids! I hope you keep making more!!! Yours are by far the best on youtube! :)
You can't listen, that's why
@@lemondrop8203someone’s never experienced a bad teacher
Thanks,dave. At this current time, i have a hard time learning about frictional force in orthodontic. And ur explanation makes me a little bit confidence. I understand the first 5:30 minutes,the rest remains a question for me. Thx
thank you dave my physics teacher didn't explain in this way as you explained . thank you very much
This Guy explained these concepts in just 8 minutes which I am Trying to understand from 2 weeks
Your videos are so helpful, thank you so much!
Lots of new ideas thank you . It's relevant in my study
Thanks for helping Dave
thank you so much for sharing your knowledge with the world :D! now it all makes sense :)!!
We could see how much effort you put into creating a video.
Super.👍
We A4Q team with your growth.
Full support 💪
Concepts are simply built...Thanks Sir..
This is my first video of yours and I subscribed as soon as I saw it at a glance 😊
NOW THIS IS CLEAR THANKS PROFESSOR
Thank you, You’ve helped me understand the difference between the frictions.
7:05 aren't the x & y components mg*csc(theta) and mg*sec(theta) respectively? The trig here isn't checking out for me.
? to denote x-component of mg
sin(theta) = mg/?
?*sin(theta) = mg
? = mg/sin(theta)
? = mg*csc(theta)
Super! You made the subject simple! Thanks
Wow..ur teaching is superb with practical learning
exactly what i needed before my test! thanks!
Thank you so much, I was stuck on a question and this video helped me a lot!
czcams.com/video/DE6QvdAO9Qw/video.html
Reason of why static friction is more than kinetic or dynamic friction
i think there is an error in checking comprehension. if the object is at rest, we wont know whether it moves unless we look at the static friction coefficient (as opposed to kinetic friction as stated)
thank you so much! you saved a university newbie!
1:31 "This attractive interaction can hinder motion to some degree" This can easily be taken out of context.
Thank you. It helped a lot .
thank you man, i am teaching my nephew vectors and this video helps a lot to illustrate parts of the whole idea. thank you.
czcams.com/video/DE6QvdAO9Qw/video.html
Reason of why static friction is more than kinetic or dynamic friction
6:54 I wonder if the Fnet=mgcos(theta)-Fsf resulted in a negative number (meaning the Fsf is greater than the mgcos), then what will happen? Will the box stay at rest or will the box move upwards? Depending on the context though, i'd guess the box would remain at rest.
Great explanation - thanks
thank you i really understand friction so easy
I was in tension abt tomorrow's exam but your intro made me free and calm
Great explanations!!
Professor please make a video on tension it is an important topic please make it I love your teachings
Thank you for illustrating perfectly
Thank you man, you nailed it. My teacher can’t even explain it clearly 🙄
Wow thanks alot ,it was really well explained
Professor Dave, I have a question! If friction is caused by forces of attraction between atoms on a molecular, and electrostatic attraction is one of of these forces of attraction. Does this mean that friction can change based on the charge of the object?
Is it specified that the attraction is really electrostatic?
Subbed not only because useful information but because Subaru 😎
thank you for explaining clearly
Thankyou Professor Dave!
Bruh, how does this guy manage to learn something that is hard to explain in such ease and how long did it took for him to learn this stuff?
when the mass of an object increases the normal & frictional force increases do the static force increases as well?
Very precise
thanks, really helped
Hello! In the comprehension check you use Fnet= mg sin theta - Ff, I am confused as to why you are using subtraction instead of addition.
Thanks!
it's true, it could be addition as long as you then make the frictional force negative, we just need opposite signs on the two horizontal forces as they are in opposite directions. in the end, as long as the signs make sense you're all good!
There is no certain direction for a frictional force to be acted. It is always resistive to a motion or to an attempt to the motion. When the block moves or tends to move down, frictional force would act up the incline. When the block moves or tends to move up, the frictional force would act down the incline. Thanks.
Is it safe to assume then, that in problems like these as long as the box is going downwards the frictional force will be negative ?
KB yes. It’s in the opposite direction of the motion so it’ll be negative.
If I wind a rope around a spool body, how many winds do I need to get a frictional grab where it can not slip? Thanks
@professor_dave_explains do you still stands by the statement that rougher surfaces have more friction?
Nice explained.
which is correct, is it @6.31 : net force = kinetic friction + mg sin theta or @6.53 : net force = mg sin theta - kinetic friction
confused help
Hello. I'm just confuse because I read the book named "Conceptual Physics" that says that Increasing contact points doesn't add to the friction. Can someone clarify thanks
I'm not positive but I think it has more to do with the force of gravity on the contact points than the points themselves. If I have two boxes of the same size on the ground (therefore both boxes have equal contact points with the ground) and one weighs more, the normal force will be greater, and therefore the frictional force will also be greater.
This model works very well for hard surfaces. I wonder how the contact area and other factors start to be important when analyzing friction in deformable surfaces like rubber or human tissue? Would be interesting to know :)
But Sir how we will know what is the value of cos 35° and sin 35°?
now I understood the difference between static and kinetic. whoa!!
very helpful!
I have a question: Why is static friction used to walk forward? I know our foot pushes backwards, and the friction lets us go forward, but i thought that static friction only resisted the initiation of motion. Is there an another definition for static friction or am i just not understanding this concept correctly?
It is only locally that static friction opposes the initiation of motion. Locally at the point of contact between two objects. The static friction in this example, is what stops your foot from moving backwards as you push it backwards while trying to walk. If you were on a truly frictionless surface, your foot would slide backwards and you would run in place if you tried to walk.
Think of the Earth's surface a "work mirror". You push backward on the ground, by pushing your foot backward while it is in contact with the ground. By Newton's third law, the ground also pushes forward on your foot with an equal and opposite force. The force on the ground by your foot, cannot practically do any measurable amount of work on the Earth, because of the Earth's inertia is so large that its motion due to this force is immeasurably small. Instead what happens, is that the ground reflects this force back to you, through its third law pair of this force, as the ground applies a forward force to your foot, while your body moves.
Thank you so much sir!!!!
I love you and your channel so much dude
Thank you sir!
So why does static friction have a maximum value? What causes it to suddenly stop increasing?
What If I have a problem where it's supposed to be solved by work kinetic theorem AND THEY JUST GIVE THE FRICTION, MASS AND DISTANCE AND ASK ME TO FIND THE INITIAL VELOCITY. WHAT I NEED TO DO?
Sir why are we subtracting friction forces from mgsin35 to have friction net force instead of adding to satisfy the static condition of forces in the x- axis
Friction is in another direction it must be taken away
Why is coefficient of friction = the angle the object is sliding at?
Isn't it determined by the surfaces smoothness?
Amazing.
Thank you 💜
most welcome Dave
Oh sir...
Thanks for saving me ... Actually i love physics but the concept of cofficent "i was unable to understand 8t properly but after you video .. everythings is clear...
Thanks sir! !!!!
Coefficient just means a number multiplied by another number. Like in y = A*x^2 + B*x + C, the A and B are examples of coefficients.
COOL SUBARU CLIP! really piqued my interest. are you a subaru driver, dave?????
FYI for people watching this, Fstatic is NOT always greater than Fkinetic. The magnitude of Fstatic depends on how much other force acting parallel to the surface exists. Fstatic can be as much as 0 N if there are no forces trying to slide the object across the surface.
It is mu_static that is always greater than mu_kinetic. N*mu_static sets the upper limit for how large Fstatic can be. Whereas N*mu_kinetic sets what the friction force will be, in the event that there is existing sliding veocity.
thank you, sir. You are so gooooood...
Helpful :) thank you.
ya really
Many thanks.
Does the net force depend on the direction of motion if the body or is it always Fnet= mgsin@ + Ff
But why does static friction push back exactly as much as I push the object? And why is there a maximum? Why is dynamic friction always weaker?
Lot of thanks
Very good
Thanks for explaining Dave but what if there is no applied force and there is a friction force? Does that mean the object will move the other way
No
Thank you professor
Professor Dave Explains , The Classic Vintage Intro.
The best intro ever seen😄👍🏻
Can you please add a video about free body diagram in detail
Can work done against non conservative forces get stored in the form of potential energy?
oh man, good question. i can't think of how that would work but i'm sure there must be some example.
Professor Dave Explains the Induced magnetic field in a coil is a non conservative field. Still work is stored in the form of magnetic potential energy. Is it the same thing? Thanks :)
Can't. That work will be wasted mostly as heat. This is what the meaning of "nonconservative"
It is very clear that, any conservative force must be accompanied with a kind of potential energy. But Nonconservative forces are not. By the way, conservative force is defined by the equation of F = dU/dx. Where dU is the differential of potential energy. Work done against a conservative force will result an increase in the kind of potential energy and vise versa. Work done by a nonconservative force will definitely waste the energy which is not reversible as dU. Thank you Sir.
I LOVE U PROF. DAVE !!!
Thanks!
highly recommended☺
May I have a question. At 1:27 you said the interaction between atoms in the object and atoms in the surface is an attractive interaction. But shouldn't it be repulsive instead? Because the interaction here is between electrons of the object's atoms and electrons of the surface's atoms, both are negatively charged, so they should repel each other instead of attract, right?
And if they repel each other, logically this interaction should help facilitate the motion by pushing the two surfaces away from each other. But in fact, motion is hindered. Could you explain how it works?
Atoms that are stable have no net charge.
The atom consists of protons as well which cancels the effect of negatively charged electrons. In an atom (which is not an ion) the number of protons and electrons are equal and both of them have the same charge.(i.e charge in a single proton= charge in a single electron) . ( This is 100% true)
But the thing is that, even if two charged bodies are interacting still friction will act upon them. Considering that the bodies are big(big enough that we can see them). This is classical physics. Here we deal with objects that are not very small. (Although I am not 100% sure about this one)
Could you talk about Law frame of inertia
Thank you
Can anyone explain why add? 6:27
wow thank you you the simply the best
Question - how can F=ma if F is a variable? In a previous video we see how a puck requires very little force to move across ice, but put that same puck on sandpaper and it'll require more force to move it in the same manner. Is it just that when dealing with additional forces such as friction, "F=ma" becomes Fnet=ma?
It always is Fnet = m*a. We just get away with omitting the subscript of "net" when we are only dealing with one force that makes a difference in the object's acceleration.
When the puck moves across the ice, there are two significant forces which you ignored completely. Namely, the weight of the puck, and the normal force of the ice pushing upward on the puck. These forces add up to zero, by the nature of the normal force, since the normal force will be as large as necessary within the strength of the materials, to prevent penetration. Because these forces add up to zero, they cancel out of the equation of Fnet=m*a.
Definition of force is that:-
F=ma
But isnt friction also depends on the size of the base of the object? A bigger box will touch more things on the floor a small box will touch less, regardless of the mass.
Someone explain
Hi Dave, It has been like 10 years since I did trigonometry, so pleaase forgive my ignorance! How did you come up with mg Cos TH and mg Sin TH?
SOHCAHTOA! you have to make a triangle and rearrange the definitions of the trig functions. i go over it in one of the earlier tutorials in the classical physics playlist, i think the one on vectors. but i will go over it in much more depth in my upcoming trigonometry tutorials!
Thank you!
I really appreciate you tnx so much
In the comprehension check, if the block begins at rest, why don’t we account for static friction before kinetic?
anyone know why the kinetic frictional force in the comprehension is being multiplied with the y component of gravity as opposed to the x component?
I think it's bc we r finding the acceleration and as the box accelerates the weight cos opp or slow it that's my understanding
Friction does not, depends upon mass,and contact area? How it is possible because as mass and contact area increses their is more adhesion between surfaces of two objects, so more force is required and so equal and opposite reverse friction force operate. Kindly clear my doubt
The unitless friction coefficient is independent of mass and surface area. It depends on the identities of the two surfaces, the conditions of the two surfaces, and whether the friction is static or kinetic.
From a first order overview of friction, it is independent of surface area. The surface area ends up "cancelling out" of the equation.
The friction force itself, will indirectly depend on mass, because it depends on the normal force, which is usually a reaction force to the object's weight, in some form or another.
How did you get so good at solving, what did you do when you were a student... I want tipsssss as many as the s' s i put
I think he has used calculator. How can someone know the values of sin 35 and cos 35 and use their decimal values in an equation? The equation becomes long and we have multiply big numbers. I think giving angles like 30,45 or 60 is good because their values are easy to work with at the time of calculation.